The present invention relates generally to leak detection systems for detecting fluid leaks from fluid storage tanks using distinctive tracer compounds to provide detectable components in a fluid leak from the tank. The present invention also relates to a system for soil gas sampling, analysis and reporting to determine the presence and magnitude of a fluid leak from a fluid storage tank. More particularly, the present invention relates to an aboveground system that collects sub-surface soil gases for analysis without the need to penetrate the soil. The present invention exhibits utility whether used to detect leaks in underground fluid storage tanks, aboveground fluid storage tanks or in fluid transfer pipelines. For purposes of clarity all such vessels shall be referred to as fluid storage tanks. The fluid stored in the fluid storage tank may be either a liquid, such as gasoline, or may be a gas, such as methane, natural gas, butane, propane or the like.
The present invention further provides a tracer leak detection method that relies upon the addition of a highly volatile liquid chemical to the fluid contained within the fluid storage tanks. These tracer chemicals provide a unique and identifiable analytical signature. This signature is then used to detect and localize very small leaks from fluid storage tanks. When a leak occurs in the fluid storage tank, the leaking fluid will contain a quantity of the tracer chemical. The tracer escapes from the fluid by vaporization and disperses into the surrounding soil by molecular diffusion. Soil gas samples are collected from the subsurface soil area by withdrawing a volume of soil gas through the surface of the soil, including any man-made surfaces thereupon, e.g., concrete, asphalt, etc. Gas chromatography is employed on the collected soil gas samples to reveal the presence of the gas phase tracer, if any is present in the collected sample. The selection of tracer is important to insure that it provides a unique signature for gas chromatography.
The types of tracer chemicals useful in the present invention are more fully described in U.S. Pat. Nos. 4,725,551 and 4,709,557 issued to Glenn Thompson (hereinafter the xe2x80x9c551 Patentxe2x80x9d and the xe2x80x9c""557 Patentxe2x80x9d, respectively) the disclosures and teachings of which are expressly incorporated herein. Ideally, the selected tracer is normally a highly volatile organic tracer having a boiling point in the range of about xe2x88x9272xc2x0 C. to about 150xc2x0 C., with the preferred compounds being of the group known as fluorocarbons.
A wide variety of different soil gas sampling leak detection methodologies are known. Common to each of these methods is the provision of some means for collecting soil gas samples. For example in each of the ""551 and ""557 patents a sampling probe is vertically disposed in the backfill material surrounding an underground tank. The sampling probe has a plurality of apertures to permit soil gases to enter the probe for subsequent evacuation. It is also well known to employ carbon adsorbents in the sampling probe to collect hydrocarbons or tracer chemicals for subsequent collection by desorbing from the carbon and analysis of the desorbed gas. Similarly, U.S. Pat. No. 4,754,136 discloses that a neutron backscatter gauge may be lowered into the sampling probe to determine whether the probe contains volatile organic material indicative of a leak from a fluid storage tank. A positive neutron back scatter reading is verified by running a gas chromatogram on a soil gas sample collected from the sampling probe and comparing the chromatographic signature with the known material in the fluid storage tank.
Each of these leak detection systems require that a soil gas sample be taken from the sub-surface sampling probe then analyzed on a gas chromatograph. Each of these systems require that some type of probe be inserted into the sub-surface soil region proximate to the fluid containing tank in order to sample soil gases for leak detection. None of these systems, however, provide a method or apparatus for sampling soil gases for leak detection that does not require insertion of probes, housings or other devices for collection of the soil gas samples. Moreover, none of these conventional systems offer an apparatus and method for collecting sub-surface soil gas samples from above the surface of the soil. It has been found desirable, therefore, to provide an apparatus and method for collecting sub-surface soil gas samples above ground by evacuating soil gases from the soil surface, passing the gas sample through a filter and onto an adsorbing bed specific for adsorbing distinctive tracer chemicals present in the sub-surface fluid storage tank.
Underground and above-ground fluid storage tanks and fluid pipelines interconnecting such storage tanks with dispensing pumps typically contain environmentally hazardous chemicals, such as hydrocarbon fuels or solvents. Some portion or all of the tank and pipelines often reside in the sub-surface soil that is covered by a man-made material, such as concrete or asphalt. Conventional leak detection systems require sub-soil insertion of a field of probes or wells that penetrate into the underground area proximate the pipelines or fluid storage tanks. Soil gas samples are obtained either by evacuating samples from the probes or wells or by adsorbing soil gases onto an adsorbent bed placed within the probe or well and removing the adsorbent bed from the probe or well for analysis. Where the fluid storage tanks and/or the pipelines are located in regions covered by man-made materials, insertion of probes and/or wells into the sub-surface soil area is difficult, expensive and labor-intensive.
It is, therefore, a principal object of the present invention to provide a system for determining whether a fluid storage tank is leaking without the need to penetrate into the sub-surface soil area. This objective is achieved by providing an apparatus which is usable above-ground for sampling sub-surface soil gas samples for analysis of the presence of a distinctive chemical tracer present introduced only into the fluid storage tank. The present invention comprises an apparatus that includes a sled base consisting of a planar quadrilinear, or ski shaped plate (hereafter called the xe2x80x9cplatexe2x80x9d) having an upturned leading edge and having an annular opening passing through the plate and centrally positioned on the plate, a tubular manifold in fluid flow communication with the annular opening and passing upwardly therefrom, to a sample collection means. The sample collection means is comprised of a vacuum pump, a filter, and a sample tube containing an adsorbent material specific for the distinctive tracer introduced into the fluid contained within the fluid storage tank. A flow meter, to enable monitoring the amount of sample that passes through the adsorbent tube, may be used at the out let of the sample collection means. A pressure gauge or vacuum gauge placed between the pump and the adsorbent tube may also be used to monitor the rate of airflow through the adsorbent tube.
The sample collection means may be mounted on the plate, in which case it is connected directly to the opening in the central portion of the plate. Or, the sample collection means may be mounted remotely from the plate, either carried in a backpack or mounted in a vehicle, in which case the sample collection means is connected to the opening in the central portion of the plate by means of an appropriate length of small diameter tubing sufficient to span the distance from the plate to the sample collection means. Also, if the sample collection means is mounted remotely from the plate, it may be connected directly to a gas chromatographic means for analysis of the chemical tracer. If the sample collection means is not connected directly to the gas chromatograph, then the sample tubes are removed manually from the collection apparatus and manually connected to the gas chromatograph for analysis.
These and other objects, features and advantages of the present invention will become more apparent to those skilled in the art from the following more detailed description of the preferred embodiments of the invention taken with reference to the accompanying drawings.